High-frequency apparatus



06L 1946- w. M. KELLOGG v HIGH FREQUENCY APPARATUS Filed nee. 11, 1941 2 Sheets-Sheet l Fla:

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lM/ENTW nmmwac (344 Oct. 29, 1946. w KELLQGG HIGH FREQUENCY APPARATUS 2 Shets-Shet 2 Filed Dec. 11, 1941 INPENTOR 7 8y (M /(ELM Eel I I I I I I u. I 1 I I I I I I I I I I 0 I I I I I I I I I I I I I I I I I I I I I a I .111)!!! I! IIIIII/IlIl/lI/ll ATTORAE'V incoming line Patented cs. 29.1946

orrica mGn-Fnn UnNcr maaa'rus William M. Kellogg, Morrlstown, N. Lgassignor to Bell Telephone Laboratories,

Incorporated,

New York, N. 2., a corporation of New York Application December 11, 1941, Serial No. 422,510

This invention relates to amplifiers fo use at ultra-high frequencies and particularly to tuning, impedance matching and neutralizing circuits therefor.

An object of the invention is to provide an amplifier for ultra-high frequency radio waves which is simple in construction and readily adjustable for operation at different frequencies.

A further object of the invention is to provide a neutralizing system for ultra-high frequency amplifiers.

- In the operation of. amplifiers and similar circults. in the ultra-high frequency range, it has been found that circuits having distributed constants are superior to lumped constant circuits for use for tuning, impedance matching, neutralizing, and the like. For example, one method of. tuning] the input of an amplifier and matching its-impedance to the incoming line is to connect to the amplifier input a short-circuited section of transmission line the length of'which is so adjusted that in combination with the input impedance of the amplifier it acts as a quarter wave-length line at the frequency, of the waves to be amplified.

with such an arrangement the incoming line may be tapped onto the short-circuited line at a point where'the two impedances are equal. Electrically,

such 'a system operates very satisfactorily. Also where the amplifier is to be used only at a single frequency the apparatus can be quite readily constructed and adjusted for such satisfactory opv eration. However, where thesystem is to be ad- :lustable to permit operation at any of a number of frequencies,.there are certain structural dim culties. Among these is the problem of providing for the variable connection between the incoming line and the quarter wave line particularly since flexible lines are not entirely satisfactory for waves in the ultra-high frequency range.

In accordance with a feature of the present invention there is provided a system in which the is connected directly to the am plifier input and there is further provided a stub line of adjustable length which may be connected to the incoming line at various points along the length of the latter. The characteristic impedance of this section of input line is the same as that of the line from which the amplifier signal 1 is derived. In this system the amplifier is tuned J by the line formed by the portion of the incoming line between the amplifier and the tapping point of the stub line in series with the stub line and at the same time impedance matching is. achieved by the adjustment ofthe tapping point. Such a system is the electrical equivalent of the system 4 Claims- (Cl. 1791'i1) 2 just described and at the same time is readily capable of adjustment for operation at different frequencies. Such systems are not onlysuitable for coupling to the input of an amplifier but also for output and interstage coupling. In accordance with another feature of the invention the grid to plate capacity of an ultra-high frequency amplifier is neutralized by means of a short-circuited two-wire line connected to the grid and plate. This line is surrounded by a cylindrical shield which forms on each side of the two-wire line a substantially concentric line.

This invention can be more readily understood by reference to the following detailed description of one embodiment ofthe invention in an ultrahigh radio frequency amplifier as shown inthe 1 drawings in which:

Fig. 1 is a schematic circuit diagram thereof;

Fig. 2 is a plan view;

Fig. 3 is a front elevation, partly in section; Fig. 4 is an end view partly in section;

Figs. 5 and 5A are detailed views of the stub line ll, Fig. 5 being an end elevation and Fig. 5A aside elevation; v

Fig. 6 is a detailed plan view (in'enlarged scale) taken along the line 6-6 of Fig. 3;

Fig. 7 is a detailed front elevation of the portion shown in Fig. 6;

Fig. 8 is a detailed end elevation taken along the line 8.-8 of Fig. 6 and showing the construction of the filament by-pass condensers; Fig. 9 is a detailed inverted plan view of the filament by-pass condensers; and

Fig. 10 is a detailed exploded view of the blocking condenser 34. v Fig. 1 shows in a somewhat conventional schematic circuit form theultra-high frequencyamplifier of the present invention, the construction ofwhich is illustrated in the other figures. This amplifier comprises a triode vacuum tube ll en- 'closed in a shield comprising a portion l2 surrounding the tube itself and a section portion I3 closing the top of the tube shield and also enclosing the neutralizing line, tobe described later. 4 The radio frequer Y input'to the tube is brought in through a concentric linecomprising an outer conductor or sheath H and a tubular inner conductor II. The outer conductor is grounded tothe shield l2 and connected to the cathode of the tube H through the direct current blocking condensers l6 and 26. A short-circuited stub line H is provided to tune the input circuit and provide proper impedance matching for the input.

' The stub llne'comprises an outer conductor or to shield l1, an inner conductor i8 anda short-cirplanation though in the actual construction of the other figures it is fixed, thus fixing the length of the stub line.) The shield I'I contacts the outer .conductor ll of the input line and the inner conductor l3 contacts the inner conductor l5 of the input line.

The stub line H is movable along the input line so that the length of the short-circuited section from the grid of tube H to the shorting member l9 may be adjusted. This provides a tuning section between the grid connection and the short-circuited terminal which when adjusted to thaequivalent quarter wave-length of the input oscillations in eflect tunes the amplifier input circuit, At the same time the input portion of the line "-45 is in effect tapped into this resonant line section at the Junction of the line l4-l5 and the stub line II. By adjusting the reactance of the stub line H, i. e., its length is determined by the position of the shorting member l9, it is also possible to obtain a proper impedance match for the efllcient termination or coupling of the input line.

Since the latter adjustment for impedance match is somewhat less critical than the tuning adjustment, it is possible, particularly where the amplifier is intended for operation over a narrow frequency range, to determine by'preliminary calculation and trial the necessary length of the stub line I! and fix the position of the member Hi. This is done in the embodiment shown in the other figures, though, of course, applicant's invention is not limited to such an arrangement.

The equivalent electrical circuit, that is a quarter wave-length line for tuning with an intermediate tap for impedance matching, is familiar to those skilled in the art. However, applicant's structure avoids a serious handicap of the previous arrangements in which it was necessary in order to make the impedance matching adjustment to use a flexible section of incoming line. Such an arrangement is undesirable, particularly when operating in the higher frequency ranges.

The plate or output circuit of the amplifier is tuned and efilciently coupled to the outgoing coaxial line 2425 by a similar arrangement. This comprises the coaxial line having an inner tubular conductor 24 connected at the inner end to the plate of the tube ll through a blocking condenser 34 and an outer conductor 25 connected to the grounded shield l2. The blocking condensers l6 and 26 serve to connect the cathode of tube ll. The adjustable tub line 21, which is similar to the line I l, is also provided and comprises a shield 21 contacting the outer conductor 26, an inner conductor 28 contacting the inner conductor 25 and a shortingmember 29. The direct current plate supply is brought in through the insulated wire 30 carried within the tubular inner conductor 25. The line 24-25 maybe used for interstage coupling in which case it leads to a second amplifier and is terminated in a similar manner to the input line I l-l 5. a

The tube II is neutralized to prevent the generation of spurious oscillations by means of the balanced line 3l32. One side 3| of this line is connected to the grid of tube II. The other side is connected to the plate of tube ll through the blocking condenser 34. The line 3l-32 is adjustably short-circuited by the member 33 so that its inductance can be adJusted to give a reactance q al othat of thegrid to plate capacity, thus neutralizing the en'ect of the latter.

The adjustment may also be made to cause the amplifier to operate as a regenerative amplifier. if desired.

The line 3l-32 is enclosed in the shield l-3. Each side of the line 3l-32 acts as the center conductor of an approximately concentric line of which the cylindrical shield I3 is the sheath. This presents an impedance from the plate and from the grid to the sheath l3 that isdetermined by the characteristic impedance and length of these concentric lines. The length is determinedby the shorting member 33 which is extended to contact the sheath l3. Since the cathode and sheath are at substantially the same radio frequency potential the grid and plate circuits are additionally tuned by this system. Therefore, these concentric lines should be self-resonant or have sufllcient inductive reactance to partially or wholly resonate the grid-sheath and plate-sheath capacitances With the shorting member 33 in the position that permits the balanced line 3 l-3Z to tune the grid-plate capacitance to resonance. These requirements place a restriction on he diameters of the neutralizing rods 3l and 32 and the inner diameter ofthe sheath or shield I3. It is preferable that there be approximate equality of the characteristic impedance of the rods as a balanced line or as individual unbalanced (concentric) lines. Accordingly,'at any setting of the member 33 less than a quarter wave-length a triangle of approximately equal inductive reactances is presented to the tube I i. This provides the reactances desired for a tube such as the Western Electric 703A vacuum tube, the interelectrode capacitances of which are approximately equal. For a tube of different characteristics, different line parameters would be preferred.

In neutralizing the amplifier, the plate voltage is removed and with a high signal input the input and output stub lines I! and 21 are set for maximum output while the member 33 is adjusted for the maximum ratio of input to output. When so neutralized, the input and output circuits can be retuned independently by a readjustment of the stub lines ll and 27.

For the actual structure of a practical embodiment of my invention reference is made to Figs. 2 to 10 of the drawings in which the same reference numerals are used throughout for like elements. Referring first to Figs. 2 and 3, the amplifier is built on a panel or base 48. Above this base and secured thereto by screws i a shielding housing l3. This shield 33 is made square in cross section for mechanical reasons but is the substantial electrical equivalent of a circular shield as regards its cooperation with the neutralizing rods 3| and 32 in tuning the grid and plat circuits.

The amplifier is supported mainly by the housing l3 as is more clearly shown in Figs. 6 to 9. The input concentric line comprising the sheath I4 and the inner conductor I5 is supported in the right wall of .the housing l3. For this purpose the inner end 4| is turned down forming a reduced portion and a shoulder which is mounted in a hole in the wall 42 by a press fit. A disc insulator 43 is mounted in a recess in the inner end of the sheath It by means of a spring retainingring 44. The inner hollow tubular conductor I5 is mounted in a centrally located hole in the disc 43 and secured there by the nut 45.

r Clamped on the end of the conductor I5 is a clamping block 36.

The clamping block 43 carries an L-shaped 81 and 80 mesh with bracket 41 and the plate terminal socket 40. The

neutralizing rod 3| is carried by the bracket 41.

of the conductor 25 at a point of low radio irequency impedance as shown in Fig. 3 thus simplifying the filtering of the direct current circuit. A clamping block 56 is mounted on the inner end of the conductor 25. Like the block 46, this block 56 carries a neutralizing rod 32 and the socket 50 for the plate terminal or the tube II. However, the socket 48 is directly mounted in block 46, while terminal 58 is mounted in the block 56 through the medium of an insulating bushing to form the blocking condenser this construction.

Referring to Fig. 10, which is an exploded view or the condenser 34, the socket 50 is screwed onto the threaded end of rod 00. The other end GI is of reduced size forming a soldering terminal for the direct current lead 30. A bushing 62 fits over the intermediate portion of the rod 60. This bushing 82 is of a lava type insulating material which is first coated with silver and then copper plated, both inside and out. An externally threaded metallic bushing 63 fits over the insulating bushing 62. The rod 50 and bushings 62 and63 are sweated together. Then the bushing 03 is screwed into the tapped hole 59 inthe block 55. In this way the plate of the tube II is capacity coupled to the neutralizing rod 32 and the inner conductor 25. The rod 80 and bushings 62 and 63 form the blocking condenser 34. It will be observed that the conductor 25 is clamped in a split portion 0! the block 55 by means of the screw 64. A similar construction is used for clamping the block 40 to the conductor I 5.

An assembly of cathode circuit condensers I6 and 26 is also mounted in the shield". These comprise a mounting plate 10 screwed to angles 69 suitably mounted on the inner walls of the shield I3. Two irregularly shaped plates H and 12 are screwed to the plate 10 and separated therefrom by the sheet of mica 13. Insulating washers 14 prevent the screw heads from making electrical contact with the plates 1| and 12. Soldering terminals 1 I .I and 12.I are provided on the plates H and 12 respectively, for connecting the leads which furnish ode of the tube II. Cathode terminal sockets 15 and 10 for the tube II are mounted on the plates 1I' and 12 respectively.

The tube- II is mounted below the panel 40, being supported from the sockets 48, 58, 15 and 16 by its electrode terminals. The shield l2 surrounds the tube II and is provided with a removable cover I2.I for access to the tube. v

. The short-circuit member 33 is mounted in the shield I3. This is provided with a wine: 82 which contacts the rod 32.. v A similar wiper, not visible in the drawings, contacts the rod it. The plate member 33 is also provided with brushes 83 which make contact with the inner surface'oi the shield I3. A block as is attached to the plate 43.- A shaft 88 isJcurnaied-in this block at and carries two pinions .81 and 88 within the shield I3 and a knurled knob 89 outside. The pinions racks 90 and 0| secured to the inside oi the shield I3. Thus by turning the knob 09 the osition of the plat 33 and consequently-the 34. Fig. 10 shows the teeth of the respective eflective length ot'the balanced -neutralizing line and the unbalanced plateand g-rid lines may be adjusted. A pointer 02 and sc'al ive anindication of the adiustmena' Figs; 5 and 5A show the construction "of the stub line I1, the stub line 21 beingidenticalithere- "to. This comprises an outer housing orshield I00 formed largely of sheet metal but having two solid end blocks IOI soldered to the sheet'lmetai portion. The lower end of eachof these end -blocks IN is machinedto form a tongue I02,

which rides in the slot J in the top of the outer conductor I4. Riding on the inside of the conductor I4 is a shoe I03 vthat is fastened to the end blocks IN by means of the machine screws I04 and springs I05. A wiper I08 contacts the inner conductor I5. This wiper is carried; by a stem I8 forming the inner conductor of the stub line I1. The stem I8 is carried by two guide blocks I01 to which it is riveted. The assembly of blocks I01 and stem I8 are secured to the casing I00 by means of machine screws I08 and I09. The screw I09 in addition carries a strip IIO the-lower end of which is bent outwardly and pointed to iorin an indicator III. This indicator cooperateswith the scale H2 to indicate the corresponding end of said shield to 'said heating current to the cathsaid adjustable tube amplifier having a cathode,

of spurious oscillations,

cathode, and an adjustable device forming a short circuit at the other said two wires and a point on said shield spaced from said corresponding end thereof, the spacing of the wires of said two-wire line with respect to each other and to said shield being such that said adjustable device simultaneously controls the length of said substantially concentric lines to tune the grid and anode circuits to the operating frequency and the length of said two-wire line to prevent the generation of spurious osciliations.

high frequency amplifier, a vacuum an anode, and a control grid, a two-wire line having a set of terminals connected to said anode and control 2.Ina

grid, an adjustable short-circuiting element for said line whereby the regenerative action or said tube may be controlled to prevent the generation a shield surrounding said line and so spaced therefromrelative to the spacing of the wires of said line that each of said wires forms a substantially concentric line with said shield, and circuiting said wires to said shield to tune the grid and anode circuits to the operating frequency of the amplifier.

3. In an ultra-high frequency amplifier according to claim 2, means for simultaneously ad-, iusting said adjustable short-circuit element and device.

frequency amplifier. a vacuum 4. In a high ananode and a control tube having a cathode,

' grid, 2. two-wire line, a shield surrounding said line and so spaced relative to said line and to the spacing between the two wires thereof as to form a substantially concentric line with each set of terminals of an adjustable device for shorteach of said two wires and said shield, and con- 10 stantially concentric lines formed '8 trol means for adjusting the position of said plunger in said shield to simultaneously adjust the length of said two-wire line to prevent the generation of spurious oscillations and the subbetween each of said two wires and said shield to tune the grid and anode circuits to the operating frequency. 

